Glucagon is 29 amino acid peptide hormone produced by pancreatic α-cells in response to low blood glucose levels. Glucagon binds to a membrane-associated glucagon receptor on the surface of hepatocytes, which triggers a G-protein signal transduction cascade, activating intracellular cyclic AMP and leading to release of glucose through denovo synthesis (gluconeogenesis) and glycogen breakdown (glycogenolysis).
Unson et al., disclose polyclonal antibodies raised against synthetic peptides corresponding to two extracellular portions of the rat receptor. In the assay disclosed, polyclonal antibodies raised against amino acid residues 126-137 and 206-219 were found to block binding of glucagon to the receptor in rat liver membranes (Unson et al., PNAS Vol. 93, pp. 310-315, January 1996).
Buggy et al., discloses the preparation of a monoclonal antibody that is said to compete with glucagon for the hormone binding site of the receptor in an in vitro assay (Buggy et al., Horm. Metab. Res. 28 (1996) 215-219). In the assay disclosed the antibody, given the designation CIV395.7A, recognizes the human and rat glucagon receptors, but not mouse. In order to develop antibodies for human therapeutic treatments it is commonly necessary to perform pre-clinical efficacy and safety studies in validated rat and/or murine animal models. It would therefore greatly facilitate drug development of a therapeutic antibody and thus be highly desirable to provide a pre-clinical therapeutic antibody candidates that are able to bind rat, murine and human forms of the glucagon receptor.
Wright et al., disclose a monoclonal antibody designated hGR-2 F6 and the amino acid sequence of a Fab fragment thereof. This antibody has been raised in a mouse against the human glucagon receptor and described in the disclosed assay as a competitive antagonist at this receptor (Wright et al., Acta Cryst. (2000) D56, 573-580). The applicant has found that hGR-2 F6 binds to the rat and murine forms of the glucagon receptor with only low affinity, and no therapeutic efficacy has been found for hGR-2F6 in a diabetic rat in vivo model at high doses. In particular, this antibody was unable to reduce blood serum glucose in the rat model with any statistical significance (unpublished).
The applicant has identified a need to provide therapeutic monoclonal antibodies that will bind with high affinity to the glucagon receptor and thereby inhibit the binding of glucagon thereto, to provide effective treatments for diabetes, preferably type 2 diabetes and related disorders. Furthermore, in order to allow pre-clinical drug development of an antibody it is clearly desirable to provide monoclonal antibodies that can bind to the human, rat and murine forms of the glucagon receptor to allow obligatory pre-clinical safety and efficacy studies to be undertaken.